Loudspeaker construction



Oct'. 31, 1961` A. F. PETRIE ETAL LOUDSPEAKER CONSTRUCTION Filed Sept. 25, 1959 J2? mentor-a. Ade/are Ar/Der/, uwe R Aub/"gg,

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United States Patent C) 3,006,430 LOUDSPEAKER CONSTRUCTION Adelore F. Petrie, Camllus, and Duane Aubrey, Au-

burn, N.Y., assignors to General Electric Company, a corporation of New York Filed Sept. 23, 1959, Ser. No. 841,889 12 Claims. (Cl. 181-31) This invention relates to loudspeakers for producing sound waves in accordance with electrical signals, and more particularly to loudspeakers of the moving coil type wherein a voice coil is positioned in a magnetic iield.

A type of loudspeaker that is widely used, and to which the present invention is readily applicable, comprises a diaphragm or cone of generally conical shape, supported at its outer rim by a loudspeaker frame, and having a cylindrically shaped voice coil assembly attached to the cone near the apex thereof. The voice coil includes a Winding positioned concentrically with respect to the axis of the cone. A magnet assembly is provided for supplying a magnetic liux radially through the winding of the voice coil. The magnet assembly includes an inner pole piece positioned within the cylindrical Voice coil, and an outer pole piece positioned concentrically around the cylindrical voice coill in axial alignment with the inner pole piece. Certain loudspeakers, particularly those having a relatively small cone and intended for reproducing the higher audio frequencies, lare provided with a phasing dome which `is attached to the inner pole piece and which extends frontwardly of the voice coil.

In designing the lconstruction of a high quality loudspeaker, four important requirements to be considered are: (l) The pole pieces must be properly aligned with respect to each other so as to provide a constant-width annular gap -in which the voice coil is positioned; (2) means must be provided for preventing dust and metallic particles from entering Iinto the magnet structure; (3) a shorted turn should be electrically coupled to the voice coil, to improve the high-frequency response; and (4) the phasing dome must be accurately positioned in closely spaced alignment with the voice coil.

An object of the present invention is to provide an improved loudspeaker construction that is simple and economical to manufacture.

A further object is to provide a loudspeaker having an accurately 4positioned phasing dome.

Another object is to provide a simplle, one-piece element which functions simultaneously as a phasing dome, a pole aligning device, `a dust seal, and a shorted turn that is coupled to the voice coil winding. Other objects will be apparent from the following description of the invention, and from the claims and the drawing.

in the drawing:

FIG. l is a side View, partly in cross-sectional form, of a preferred embodiment of the invention; `and FIG. 2 is a front view of the loudspeaker shown in FIG. 1.

The invention comprises, basically, a cup-shaped element of non-magnetic material positioned over the inner pole piece of a loudspeaker and extending frontwardly of the inner pole piece, and, preferably, frontwardly of the voice coil. In the preferred embodiment of the invention, the cup-shaped element is made of electrically conductive material and has an outwardly extending flange which curves around the rear end of the voice coil and engages Va shoulder of the outer pole piece.

Now referring to -the drawing, the preferred embodiment of the loudspeaker construction comprises a frmne having a rim 11 at one end thereof and a flange 12 at the other end thereof. A cone or diaphragm 13, which may be m-ade of pressed paper or other suitable material Patented Oct. 3l, 1961 ICC and which has a generally conical shape, is attached to the rim 1'1 by means of an outer suspension 14 which may comprise a series of concentric corrugations of the outer edge of the cone 13. A cylindrical voice coil form 16 is attached to the cone -13 near the apex thereof, and is aligned on the axis of the cone 13. The voice coil form 16 may be made from paper or a non-magnetic metal such as aluminum. An linner suspension 17 is attached between the flange 12 and the voice coil form 16, and may be made of impregnated cloth or other suitable material, arranged in concentric corrugations. A voice coil winding 18 is wound onto, or is otherwise attached to, the form 16, the axis of the winding 18 being aligned with the axis of the form 16 and the cone 13.

A magnet structure 21 comprises a front plate 22 attached to the flange 12, a hollow cylindrical permanent magnet 23 having one end thereof positioned against the rear surface of the front plate 22, a rear plate 24 positioned against the other end of the permanent magnet 23, and a ycore 26 extending from the rear plate 24, an end of this core being shaped to prov-ide an inner pole piece 27 of circular cross-section and positioned within the connues of the 4winding 1S. Bolts 28 or other suitable means may be used for holding the magnet assembly together.

The front plate 22 is provided with an opening, the part thereof surrounding this opening constituting an outer pole piece 29 which is concentric with, and axially aligned with, the inner pole piece 27. The inner pole piece 27 and the outer pole piece 29 provide an annular gap 31 in which the winding 18 is located, and a xed magnetic ield is provided in this gap, in a radial direction through the Winding 18, by the permanent magnet 23 which supplies magnetic iiux to the gap Via the front plate 22, the rear plate 24, and the core 26, all of which are made from magnetically conductive material such as iron. The ends of the winding 18 are connected to a pair of terminals 32, one of which is shown in the drawing, by means of ilexible lead wires 33, one of which is shown in the drawing, the terminals 32 being attached to the frame 10 by means of insulative washers 34 held together by an eyelet 36. The leads 33 are electrically attached to the eyelets 36 by means of solder 37.

In accordance with the present invention, a cup-shaped phasing dome 40 is positioned over the inner pole piece 27 and extends frontwardly of the voice coil 16, as shown. Preferably, the dome 40 is made of non-magnetic material such as plastic or copper, and has a rounded end portion 41. It is preferred that the dome 40 extends to the plane of the rim 11, as shown. The dome 40 is held in place by the side thereof fitting tightly around the inner pole piece 27. The cylindrical side of the dome 40 may be tapered slightly to facilitate a tight iit against the periphery of the inner pole piece 27.

The loudspeaker, as thus far described, functions as follows: The output of an audio amplifier or other signal source is connected to the terminals 32, whereupon an audio signal is applied to the winding 18, and the current thereby applied in the winding 18 reacts with the magnetic eld in the gap 31 in a manner causing the voice coil form 16, and hence the cone 13, to vibrate axially in accordance with the electrical signals, thereby producing sound signals.

The dome 40 functions to fill in the space that would otherwise be present in front of the inner pole piece 27 and prevents the sound waves from the cone 13 from reecting from the inner pole piece 27, and from causing acoustical perturbances, in this space. The rounded end 41 of the dome 40 functions to reduce refraction of the acoustical waves. The action of the dome 40 can be explained in the following manner: The air gap on both the inner and outer sides of the voice coil constitutes an acoustic coupling between both sides of the cone. If the dome 40 were omitted, a resonant condition within the frequency range of the loudspeaker would exist between the ,two cone surfaces which would increase the volume ow through the air gap, thus lowering the radiation pressure at the radiating surface of the cone. In addition, the relativelyilarge surface 27 of the front of the core 26 would reiiect an appreciable amount of acoustic energy which would, if the acoustic path lengths are such that the reected energy is out of phase with the radiated energy, cancel some of the radiated energy. Both effects, the shorting eect of the air gap and the reection, would occur together and result in a marked decrease of radiation. When the dome 40 is used, the shorting air path is lengthened, its resistance is increased, and the resonant condition is made to occur at a frequency outside the range of the loudspeaker. The dome 40 also functions to prevent reflection of acoustic energy from the front of the core 26.

The dome '40, being fitted around the periphery of the inner pole piece 27, is automatically and accurately centered with respect to the voice coil form 16. This accurate positioning of the dome 40 permits the loudspeaker to be designed with a closer spacing between the dome 40 and the voice coil form 16 than would be the case if, for example, the dome 40 were attached to the front surface 27 of the center pole piece 27. This closer spacing between the dome 40 and the voice coil form 16 insures a good acoustical seal between the front and back surfaces of the cone 13, and reduces to a minimum the aforesaid acoustic coupling between the two sides of the cone 13. v

In the preferred embodiment of the invention, as shown in the drawing, the dome 40 has an annular rim 42 which extends around the lower edge of the voice coil form 16 and thence outwardly and into engagement with the inner face of an annular shoulder 43 on the rear surface of the front plate 22. Preferably, the outer edge of the rim 42 is curved, as shown, so that it readily engages both the shoulder 43 and the rear surface of the front plate 22. The rim 42 is spaced from the lower edge of the voice coil form 16 by an amount suicient to prevent the form 16 from contacting the rim 42 during operation of the loudspeaker.

The dome 40, when provided with the rim 42, performs four functions simultaneously, as has been mentioned above. The dome 40 functions as a phasing dome, to improve the sound radiation from the loudspeaker. The dome 40 and rim 42 function as an accurate spacer or jig, between the inner and outer poles 27 and 29, due to the engagement of the cylindrical side portion 51 thereof with the outer surface of the inner pole 27 and the engagement of the outer edge of the rim 42 with the shoulder 43 on the outer pole 29. The rim 42 functions as a dust seal between the gap 31 and the inner part of the magnet structure 21, due to the aforesaid engagement with the inner and outer pole pieces near the gap 31. The cylindrical side 51 of the dome 40, when made of electrically conductive material, functions as a shorted turn that is inductively coupled to the winding 18. This improves the high-frequency response of the loudspeaker as is well-known, because at the higher frequencies a relatively greater amount of current is induced from the winding 18 into the shorted turn S1, whereby the impedance of the winding 18 is prevented from rising at the higher frequencies. Such a rise in the impedance of the Winding 18 at higher frequencies, if allowed to occur, would result' in a lower amount of signal current owing in the winding 18, and this would, of course, cause reduced sound output from the diaphragm 13 at the higher frequencies.

While dust seals, centering devices, phasing domes and shorted rings have been known and used in loudspeaker constructions, and their virtues have been well recognized, it has heretofore been awkward or impossible, and relatively cumbersome and expensive, to utilize all four of these desirable devices simultaneously in a loudspeaker construction` The present invention provides a novel and practical solution to the longstanding need for a loudspeaker construction in which the desirable features of a phasing dome, centering device, a dust seal, and a shorted ring are simultaneously employed, and furthermore the invention provides an improved phasing dome that is accurately positioned with respect to the voice coil.

While a preferred embodiment of the invention has been shown and described, various other embodiments and modifications thereof` will be apparent to those skilled in the art, and will .fall within the scope -of the present invention as defined in the following claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. in a loudspeaker having a pole piece and a voice coil positioned around said pole piece, a phasing dome com prising a one-piece cup-shaped member tted around the periphery of said pole piece and extending frontwardly thereof, the bottom of said cup-shaped member being in front of and spaced from said pole piece a suicient distance for the member to function as a phasing dome for said loudspeaker, said fitting of the one-piece cup-shaped member around the periphery of the pole piece insuring accurate centering of the phasing dome with respect to the pole piece.

2. In a loudspeaker having a pole piece and a one-pieceY Voice coil positioned around said pole piece, a phasing dome comprising a cup-shaped member `fitted around the periphery of said pole piece and extending frontwardly of said voice coil, the bottom of said cup-shaped member being in front of and spaced from said voice coil a sufcient distance for the member to function as a phasing dome for said loudspeaker, said tting of the one-piece cup-shaped member around the periphery of the pole piece insuring accurate centering of the phasing dome with respect to the pole piece.

3. In a loudspeaker comprising a diaphragm of conical shape, a cylindrical voice coil attached to said diaphragm near the apex thereof, and a pole piece extending within said voice coil, the improvement comprising a onefpiece cup-shaped member fitted around the periphery of said pole piece and extending frontwardly of said voice coil and into the space defined by said cone a suflicient distance for the member to function `as a phasing dome for said loudspeaker, said fitting of the one-piece cup-shaped member around the periphery of the pole piece insuring accurate centering of the phasing dome with respect to the pole piece.

4. A loudspeaker construction comprising an inner pole piece, an outer pole piece arranged concentrically with said inner pole piece thereby providing a radial gap between said pole pieces, a voice coil positioned in said gap, and a cup-shaped member of electrically conductive non-magnetic material fitted over the periphery of said inner pole piece and extending frontwardly of said voice coil, said cup-shaped member having an outwa-rdly extending rim shaped to extend around the rear end of said voice coil and into engagement with said outer pole piece, said rim being continuous and unbroken whereby said cup-shaped member functions simultaneously as a phasing dome, a dust seal, a pole centering device, and a shorted turn for said voice coil.

5. A loudspeaker construction comprising an inner pole piece, an outer pole piece arranged coaxially with respect to said inner pole piece thereby providing a radial gap between said pole pieces, a voice coil positioned in said gap, and a one-piece cup-shaped member of electrically conductive non-magnetic material arranged to fit around the periphery of said inner pole piece and extending frontwardy from one end of said voice coil a suicient distance for the member to function as a phasing dome for said loudspeaker, said fitting of lthe one-piece cup-shaped member around the periphery of the inner pole piece insuring accurate centering of the phasing dome with respect to the inner pole piece, said cup-shaped member having a rim extending outwardly and around the other end of said voice coil and into engagement with said outer pole piece.

6. A loudspeaker construction comprising an inner pole piece, an outer pole piece arranged coaxially with respect to said inner pole piece thereby providing a radial gap between said pole pieces, said outer pole piece being provided with an annular shoulder, a voice coi-1 positioned in said gap, and a member of electrically conductive nonmagnetic material arranged to surround said inner pole piece, said member extending axially of said inner pole piece and terminating at a dome-shaped closed end thereof, said member having a rim extending outwardly and around an end of said voice coil and into engagement with said annular shoulder.

7. A loudspeaker construction comprising an inner pole piece, an outer pole piece arranged coaxially with resp ct to said inner pole piece thereby providing a radial gap between said pole pieces, a permanent magnet arranged between said inner and outer pole pieces in a magnetic circuit externally of said gap, a voice coil positioned in said gap, a cone-shaped diaphragm attached near the apex thereof to said Voice coil at an end thereof, and a cupshaped member of electrically conductive non-magnetic material arranged to fit around the periphery of said inner pole piece and extending frontwardly of said end of the voice coil, said cup-shaped member having a rim extending outwardly and around the other end of said voice coil and into engagement with said outer pole piece.

8. A loudspeaker construction comprising a first plate of magnetically conducted material and having an opening therethrough, said first plate being provided with an annular shoulder concentric with said opening on one side thereof, a core member of magnetically conductive material positioned to extend within said opening thereby forming an annular gap, a magnet connected in a magnetic circuit between said core and said first plate, a voice coil positioned in said gap, and a cup-shaped member of electrically conductive non-magnetic material arranged to t around said core at said gap and extend frontwardly of the end of said core, said cup-shaped member having a rim extending outwardly and around an end of said voice coil and into engagement with said shoulder.

9. In a loudspeaker having a pole piece and a voice coil positioned around said pole piece, a phasing dome comprising a one-piece cup-shaped member tted around the periphery of said pole piece and extending frontwardly from said pole piece a sufficient distance for the member to function as a phasing dome for said loudspeaker, said fitting of the one-piece cup-shaped member around the periphery of the pole piece insuring accurate centering of the phasing dome with respect to the pole piece, the wall of said cup-shaped member being tapered outwardly towards the open end of said member to facilitate a tight fit of said member around the periphery of said pole piece.

10. A phasing dome for a loudspeaker, comprising a onepiece cup-shaped member adapted to iit around the inner pole piece of a loudspeaker and extend frontwardly thereof a sufficient distance for the member to function as a phasing dome for said loudspeaker, said fitting of the one-piece cup-shaped member around the periphery of the pole piece insuring accurate centering of the phasing dome with respect to the pole piece.

11. A phasing dome for a loudspeaker comprising a one-piece cup-shaped member tapering outwardly towards the open end thereof and adapted to fit around the inner pole piece of a loudspeaker and extend frontwardly of the end of said pole piece a sufficient distance for the member to function as a phasing dome for said loudspeaker, said fitting of the one-piece cup-shaped member around the periphery of the pole piece insuring accurate centering of the phasing dome with respect to the pole piece.

l2. A phasing dome as claimed in claim lO, including a rim extending radially outwardly from the open end of said cup-shaped member.

References Cited in the tile of this patent UNITED STATES PATENTS 2,115,924 Fisher May 3, 1938 2,808,895 Chare Oct. 8, 1957 FOREIGN PATENTS 595,739 Great Britain Dec. 15, 1947 597,935 Great Britain Feb. 6, 1948 643,465 Great Britain Sept. 20, 1950 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No@y 3,0064 3O October 5391KI 1961` Adelore F. Petrie et al.y

It is hereby certified that error appears in ,-the above numbered patentrequring correction and that the said Letters Patent should read as "corrected below f Column 1V line 2M strike out "onepece";; line 29gV`v site;

"a". insert onepiece 4,-; line 7lY flor' "W ';\TQI,I'y read m wafdly sm., Signed andbsealed this 3rd day of April 1962;,

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

